Property-based testing of intervals and interval functions

This week Adam and Jan started developing a property-based test suite for the enclosure-based solver that is under development. The properties aim to meet two goals, first to catch bugs in the implementation, and second to make up an automatically testable specification of the implementation. Pure Scalacheck properties were chosen over properties expressed in a ScalaTest style, because they give more readable output when used in conjunction with SBT, and seem to give a terser formulation of the properties. So far, properties and generators have been written for intervals and interval functions.